Advances in electronics has allowed increased level of integration. The technology for fabrication of ICs has contributed to those advances, and has provided a vehicle for integrating a relatively large number of circuits and functions into an IC. As a result, present-day ICs might contain hundreds of millions of transistors. The transistors implement the functionality of a relatively large number of blocks, such as logic circuits, memory, processors, and communication circuits. As a consequence of the rise in the number of transistors, the power consumption, power dissipation, die temperatures and, hence, power density (power dissipation in various circuits or blocks), of ICs has tended to increase.